1. Field of the Invention
The present invention relates to a device for interrupting selectively a rotary translational movement, which is in particular used in a device for limiting the number of rotations of a mechanical shaft in an actuating system for roller blinds.
2. Description of the Related Art
In many applications a device is required for interrupting a rotary translational movement in a selective manner, i.e. controlled and/or influenced by particular boundary conditions. Although complex systems for achieving this object are known (for example using electronic control), it is extremely convenient to have the possibility of a simple and reliable solution. In the following description reference is made to an exemplar case—a device for limiting the number of rotations of a mechanical shaft—while not wishing in any way to limit the scope of the invention.
In an actuating system for roller blinds a mechanical shaft forms the main actuating member and it is required to control the rotational movement thereof. In particular, a very frequent method of control is based on the number of revolutions which the shaft performs in both directions. In said actuating systems the roller blind (curtain, shutter, etc.) is wound up on and unwound from a roller integral with the shaft such that control of the number of rotations may be converted into control of the end-of-travel position of the roller blind.
The closest state of the art for this application may be regarded as being the device 1 described in U.S. Pat. No. 3,718,215, now lapsed, from which cross-sectional figures are shown in FIG. 1 and FIG. 2. A splined shaft 10, which is integral with the mechanical shaft 55 to be controlled (shown in schematic form) and actuated by a motor 20, engages with two gear wheels 12 in turn each engaged by means of a female thread on a threaded spindle 14 on which they are able to move longitudinally in both directions following their own rotation—see FIG. 1. Depending on the direction of rotation of the splined shaft 10 (and therefore the controlled shaft) one of the two gear wheels 12 reaches and pushes a control element 16 which operates an electric switch 18 (microswitch), varying the opening/closing condition thereof—cf. the upper switch in FIG. 2. The change of state of the switch 18 is detected by the device 1 and the motor 20 is stopped. The other gear wheel 12 instead moves in the opposite direction, if necessary reaching the end of the threaded spindle 14. Clearly in the device 1 there are two sets of elements for being able to control the two directions of rotation of the mechanical shaft 55. Springs 22 push the gear wheels 12 towards the thread of the threaded spindle 14, allowing them to engage again when the latter reverses its direction of rotation. This occurs both when said wheels 12 are in contact with and push the control element 16 and when they are at the opposite end of the spindle 14 and are unscrewed therefrom—cf. FIG. 2. It should be noted that both the gear wheels 12 and the spindles 14 are made of metal. Moreover, it is clear that the gear wheels 12, the threaded spindle 14 and the springs 22 form a device for interrupting selectively a rotary translational movement, precisely that of the wheels 12 on the threaded spindle 14.
The two threaded spindles 14, respectively, extend longitudinally in the form of two rods 70a, 70b, at the end of which a gear wheel 72a, 72b coaxial therewith is present. The wheels 72a, 72b are engaged respectively with two endless screws 74a, 74b. Following installation of the motor it is envisaged adjusting the opening and closing end-of-travel positions. By means of the action of the motor, the roller blind is positioned in the desired opening position and, by means of a suitable implement, such as for example a screw driver, and assuming that the upper spindle 14 is used for adjusting the opening end-of-travel position, the endless screw 74a is turned until, by means of rotation of the rod 70a and therefore the upper spindle 14, the upper gear wheel 12 trips the upper switch 18, which causes stoppage of the motor 20. The subsequent displacement of the roller blind into the closing position and the consequent definition of the position in which the lower gear wheel 12 trips the lower switch 18, using the same method described above for the opening position, causes movement of the upper gear wheel 12 away from the upper switch 18 into a position determined by actuation of the closing end-of-travel stop. This latter position may vary depending on the type of shutter or curtain on which the motor has been mounted and depending on the requirements of the individual user. Upon subsequent opening of the roller blind, the motor will run until one of the wheels 12 actuates one of the switches 18. Therefore the rest (or non-operative) position of the upper and lower wheels 12 may be situated anywhere along the spindle 14 and may be different depending on the adjustments made. Once adjustment has been completed, the screws 74a,b keep the spindles 14 fixed.
The device 1 may be improved, so as to comprise a smaller number of parts, resulting in advantages in terms of weight, lesser complexity and lower cost.